The contractile protozoan Stentor coeruleus tranduces mechanical stimuli into receptor potentials. Upon repeated mechanical stimulation the animal habituates to these stimuli and a decrement in the elicited receptor potential is noted. We are studying the membrane mechanism involved in this tranduction process and subsequent habituation. Curare and other nicotinic blocking agents block the transduction process but cholinergic agonists and snake toxins are ineffective. By using a receptor assay based on curare binding we have found that only nicotinic blocking agents compete with curare at the binding site while cholinergic agonists and snake toxins do not. We are now isolating and characterizing this curare binding molecule as well as studying its involvement in habituation.